Field of the Invention
The present invention relates to a powerful source of ultraviolet rays and photochemical reactions that utilize the source of ultraviolet rays, and more particularly, an optical vapor phase reaction (vapor phase reaction that makes use of optical excitation) method that has a means of forming a covering film on, or of etching, a forming surface with large area, by the use of a high ontput source of ultraviolet rays.
Prior Art and Its Problems
As a thin film formation or etching technique by the use of vapor phase reactions, particularly well-known is the optical CVD method (method of chemically forming a thin film on a formation surface through decomposition of reactive gases by optical excitation) which activated reactive gases by means of optical energies. Compared with the existing method of thermal CVD or plasma CVD, this method is advantageous in that it enables to have film formation at low temperatures as well as it does not damage the formed surface.
However, the optical CVD method was possible neither to from a film with sufficiently large thickness beyond a certain value nor to form a film at a large enough speed of film growth, due to formation of a film on the surface of a window that is provided between an ultraviolet source and a reaction chamber. In the case of film of silicon nitride, the limiting thickness of the film is 1,000.ANG.. In practice, however, if the limit could be raised to at least 2,000.ANG., then the method will become industrially applicable for the formation not only of passivation film but also of reflection preventive films and gate insulating films. For this reason, some method which permits to achieve such a goal has been sought earnestly.
On the other hand, while the intensity of light from a mercury lamp depends on the pressure of mercury, the pressure is automatically fixed by the satuated vapor pressure of mercury because the amount of mercury contained in the tube for lamp is choson superfluously in order to compensate for loss in the tube.